The present invention relates to a coating composition useful in coating a continuously advancing article, such as in a pultrusion process. This coating composition can be applied contemporaneously or in-line with the pultrusion process.
The pultrusion process generally involves the steps of drawing a bundle of filaments from a source of such filaments; wetting these filaments or reinforced fibers and impregnating them with a preferably thermosetting resin by passing the filaments through a resin bath in an open tank or through a resin impregnating die; pulling the resin-wetted and impregnated bundle through a heated shaping die to align the fiber bundle and to manipulate it to the proper cross-sectional configuration; and then curing the resin while maintaining tension on the filaments. Since the fibers progress completely through the pultrusion process without being cut or chopped, the resulting products have exceptionally high longitudinal strength.
It is often desirable to apply a coating, such as paint, to the pultruded article. Typical systems for applying paint to the cooled pultruded article include spray guns and rollers. However, these systems result in the loss of a significant amount of excess coating composition and are time consuming. In-line coating apparatus have been developed which permit the application of a coating of a predetermined thickness to the hot pultruded article as the pultruded article advances through the apparatus. An example of such an in-line coating apparatus is described in U.S. Pat. No. 4,883,690, incorporated herein by reference.
The present invention is directed to a coating composition for use in coating the hot pultruded article shortly after it exits the heated shaping die. In a typical pultrusion process, the pultruded article exits the heated shaping die at a temperature of about 300.degree. F. The surface of the pultruded article is then water or air cooled to about 150.degree.-180.degree. F. before the coating is applied. However, the surface temperature of the pultruded article quickly rises to 200.degree.-280.degree. F. due to the residual heat of the pultruded article. The coating composition must be capable of withstanding these high temperatures to produce an adherent, blister-free coating of the desired thickness on the pultruded article.
It is an object of the present invention, therefore, to provide a coating composition having sufficient viscosity to provide the desired coating thickness on the pultruded article as the pultruded article advances through the in-line coating apparatus. It is a further object of the present invention to provide a coating composition for use in an in-line coating apparatus that produces an adherent, blister-free coating upon cure.